Manned Nuclear Aircraft Program By: Jack Waid

The NB-36H with a B-50 in 1955, the only aircraft to carry a nuclear reactor.

A nuclear powered aircraft! Today it sounds like a crazy concept, but was it really? Within the last

several months there was a joke in the office about this very thing. One of the historians in the office was writ-

ing a paper about the XB-70. The paper mistakenly mentions the engines of the XB-70 were nuclear powered

(should have read it was a physics package delivery platform). As things often do the joke evolved and all in

the office continue to laugh about. As it turns out the joke was much more a reality than most would believe.

The XB-70, initially designed as a Mach 3 bomber, never went into production and the two XB-70 aircraft

built saw use as experimental aircraft.

The U.S. Nuclear Propulsion Program (or Manned Nuclear Aircraft Program) began in May 1946. This after

Fairchild Engine and Aircraft Corporation, received the first formal study contract. The objective, to

determine the feasibility of nuclear energy for the propulsion of aircraft. The Fairchild project known as the

Nuclear Energy for Propulsion of Aircraft (NEPA) began at the Oak Ridge National Laboratory, TN.

Work at Oak Ridge proved building a nuclear aircraft was feasible and defined the major approaches to the

program. As a result, the Air Force and Atomic Energy Commission (AEC) joined forces in the Aircraft

Nuclear Propulsion (ANP) Program. In 1951, they contracted with the General Electric (GE) Company at

Evendale, Ohio to, “…develop a nuclear aircraft propulsion system through an exacting research,

development, design and component-test program on reactors, materials, shielding and an over-all nuclear

power plant.” 1

At the time, there appeared to be two design concepts for a “nuclear” aircraft: the Direct-Air-Cycle and the

Indirect. General Electric elected the Direct-Air-Cycle2 due to the perceived simplicity, flexibility,

adaptability and ease of handling. General Electric quickly developed high-temperature, compact, lightweight

reactors and shields required for aircraft flight. The GE Company also believed their new technology had

applicability to aerospace and ground power systems. In the 1950s, nuclear reactors were approximately the

size of two railroad cabooses stacked on one another and the performance requirements for aircraft nuclear

power plants were much more stringent than those for

electrical power generation or surface transportation

nuclear systems.

1 (U) Study (U), Author Unknown, Aircraft Nuclear Propulsion Department, Capability, General Electric, circa 1961. 2 After General Electric (GE) elected Direct-Air-Cycle Pratt and Whitney’s (P&W) Middletown, CT facility received a USAF/AEC (Atomic Energy Commission) contract for an Indirect-Cycle nuclear turbojet.

As an aside, the individual in charge of the ANP Program held both USAF and AEC positions. Major Gen-

eral Donald L. Keirn, served from 1950 to 1959 as the AEC assistant director for its aircraft reactors branch

and in the Air Force, as Deputy Chief of Staff/Development for Nuclear Systems. General Keirn was a fitting

choice, tasked by General Hap Arnold in 1941, a major at the time, to lead the Air Force Project Office devel-

oping the first US turbojet engine developed by GE.3 After his retirement in 1959, Brigadier General Irving L.

Branch wore the dual hats until the program was halted in March of 1961.

The objective of the ANP Program expanded to include the demonstration of nuclear-powered flight. Still in

1952, the Air Force decided that direct nuclear cycle engine developments were progressing well and began

construction of a power plant for the Convair B-36 flight testing and targeted for 1956 for the first flight. In

1953 the Secretary of Defense Charles E. Wilson abruptly cancelled the B-36 experimental flight program,

Wilson, a skeptic, contended “that experimental “proof-of-principle” flights were worthless unless they were

performed by a prototype for as an actual weapon systems.”4 The money slated for the project was for a weap-

ons system so, the prototype requirements leaned this direction.

Though the B-36 experiment halted, Air Force leaders managed to keep GE’s direct cycle developments

moving forward and Pratt and Whitney contin-

ued their progress. Pratt and Whitney used a

pressurized water, indirect cycle engine which

failed to progress (see below schematic). Pratt

and Whitney changed gears and began working

with the Oak Ridge on a molten salt circulation

fuel reactor, still using the indirect cycle

nuclear turbojet concept. Throughout the

testing and experimentation, Pratt and Whitney

remained behind GE in developments.

3 See AFMC/HO, “Bullet Background Paper on J-33/I-40 Turbo Supercharger Jet Engine,” 4 January 2019. After his retirement in 1959, Brigadier General Irving L. Branch wore the dual hats until the program halted in March of 1961.

4 (U) Study (U), Author Unknown, “The Nuclear Aircraft Engine,” circa 1962.

Schematic of two-loop, liquid-metal, indirect cycle nuclear propulsion system.

Though Air Force leaders cancelled developments for a B-36 nuclear powered aircraft, a Convair B-36, desig-

nated as the NB5 -36H and specially refitted to contain a fully operational nuclear reactor however, the NB-36H

did not use the reactor for propulsion.

NB-36H…Note the “radiation” symbol on the tail of the aircraft

In 1954, responding to Secretary Wilson’s desire to have a weapon system prototype, the Air Force

established a strategic weapon system requirement calling for a bomber that cruised to targets at subsonic

speeds and then fly over the target supersonically; standard turbojets for the supersonic capability augmented

nuclear engines. The weapons

system was designated the

WS-125A; GE and P&W re-

mained the engine contractors,

while Lockheed and Convair

were designated the airframe

builders.

5 ‘N’ designation used to denote a permanently modified airframe.

Lead encased cockpit

By early January 1956, GE successfully modified a J47 turbojet engine, solely to operating on nuclear power.

“The engine tested a Direct-Air-Cycle, water moderated reactor utilizing nickel-chrome clad enriched uranium

fuel elements. The reactor had an aluminum tube and shell arrangement with concentric ring fuel elements

inserted into the tubes.”6 For the first time this modified engine combined the components of a Direct-Air-

Cycle nuclear turbojet, though still not in an aircraft engine configuration. The first engine received the

designation of Heat Transfer Reactor Experiment-One (HTRE-1) (See pictures below). After the HTRE-1

came the Heat Transfer Reactor Experiment-Two (HTRE-2) and this still in 1956. The HTRE-2 was a

modified HTRE-1 designed to test alternative fuels and reactor designs under actual operating conditions. As

1956 drew to a close, the Pentagon decided the WS-125A was a drain on resources and terminated the

program. Though terminated, GE and P&W, with permission, continued nuclear engine development.

On 4 Oct 1957, the Soviet Union launched Sputnik I. This caused concern throughout the nation and many

within Congress wanted to accelerate the ANP Program in an effort to recapture national prestige. However,

in February of 1958, President Eisenhower informed Congress there was no urgency placed on the ANP

Program. He did authorize $150 million a year for ANP Program development; of which P&W received some

funds to begin limited work on a solid fuel reactor for an Indirect-Cycle engine and General Electric received

monies to continue their efforts with the Direct-Cycle engine.

The last major modification, introduced in 1958, came in the form of the Heat Transfer Reactor Experiment-

Three (HTRE-3). The HTRE-3 affixed horizontally within an aircraft and designed for flight loads. Like the

HTRE-2, the HTRE-3 utilized modified J47 engines and included basic flight control system. Specifically,

this reactor generated up to 35 megawatts, enough power to operate two J47 engines for 64 continuous hours.

This occurred during the HTRE-3’s 120-hour operational test. This reactor, before its retirement in 1958,

“made a series of all-nuclear starts, a sequence never before accomplished.”7 Previously an external starter set

the turbomachinery in motion and the engine reached full speed with conventional chemical inter-burners.

6 (U) Study (U), Author Unknown, “The Nuclear Aircraft Engine,” circa 1962.7 Ibid.

HTRE-3, left, and HTRE-2, right, now on display at the Idaho National Laboratory near Arco, Idaho. HTRE-2 was the converted HTRE-1. HTRE-1 or “Heater One” demonstrated the principle of nucle-

ar-powered turbojet engines.

In 1958, the Air Force, in an attempt to keep the ANP Program alive, introduced new mission requirement.

Known as CAMAL (continuous airborne alert, missile launching and low level penetration), it was a rehashing

of a nuclear weapons system aircraft.8 During the summer of 1959, Dr. Herbert F. York, Director of Defense

Research and Engineering in the Pentagon and other Department of Defense research officials pushed a

reorientation of the ANP Program project. These officials called for the development of a useful nuclear

turbojet capable for installation in and flown on a Convair Model 54 (the NX-2). Additionally, the aircraft

needed to reach Mach 0.8 or 0.9 at an altitude of 35,000 feet and high subsonic performance at lower altitudes.

Lastly, the nuclear engine must maintain 1000 operational hours before an overhaul. Leadership at the

Pentagon eliminated the CAMAL project before the end 1959.

8 Convair won the competition for the CAMAL airframe early in 1959 but Dr. Herbert F. York, the Pentagon’s Director of Defense Research and Engineering, soon rejected the project.

There was no question the speed requirements could be met, as David F. Shaw, general manager of GE’s

ANP Program department, told two engineering groups in January of 1961 (in Cincinnati), “It is no longer a

question of can we build a nuclear-powered aircraft system, but when can we place such a system in an

aircraft. We have reached the point that we can say that when an airframe is ready, we can have the nuclear

Direct-Air-Cycle power place ready for installation.” Pratt and Whitney recognized they were in a similar

position with the Direct-Air-Cycle engine, but were unfortunately still behind GE.

Everything changed in January 1961 as President John F. Kennedy entered his official duties and directed a

review of all military projects. Not long after, GE, P&W and Convair all received official contract termination

notices in March 1961. As the space race leapt full speed into the nation’s purview, it was not long before the

Atomic Energy Commission began working with companies to develop nuclear rocket engines (Project Rover)

and nuclear ramjet (Project Pluto). These programs had potential here on earth and in space for both military

and civilian applications.

9 (U) Study (U), Author Unknown, “The Nuclear Aircraft Engine,” circa 1962.

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For general inquiries, archives, and/or research questions, contact: R. Ray Ortensie

For heritage and exhibits questions contact: Jack Waid

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